Breaking and entering cells
DNA analysis has become an indispensable feature of modern medicine. New automated processes have been devised to speed up the preparation of tissue samples and enable diseases to be diagnosed more reliably.
The medical profession is making increased use of DNA analysis as a fast and reliable means of diagnosing infections, genetic diseases and cancer. The DNA, the patient's genetic code, is obtained not only from blood samples but also from tissue samples – for instance tumors. The only problem is that the methods used to isolate the DNA from the tissue have not yet been standardized. Scientists from the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB and the Fraunhofer Institute for Manufacturing Engineering and Automation IPA have joined forces to address this issue. Together, they are developing new automated sample preparation systems for DNA diagnostics.
“Before DNA can be isolated from tissue samples, the samples have to be disintegrated to break open the cells”, explains Dr Jürgen Bernhagen of the IGB, describing sample preparation. Current methods involve the use of aggressive chemicals, but this has one very great disadvantage: traces of the chemicals used may interfere with the reactions performed later – such as the polymerase chain reaction PCR. Thus the Fraunhofer researchers have focussed in on physical methods for tissue breakage. The samples are mechanically ground and broken up in a disposable container called an IGA tube.
The IGA tube works on the basis of a simple principle: the tissue sample is placed in a plastic container and ground using a plunger – a kind of pestle with a grating element attached to the bottom. The IGA tube is inserted in a motor unit, which moves the container while holding the head of the pestle in a fixed position. The movement generates shearing and frictional forces which separate the cells in the sample. Sub-cellular contents pass through narrow holes in the pestle into the stem of the pestle, while a filter holds back the surplus tissue. The latter remains in the container and is discarded along with the disposable tube.
“Our disposable sample container makes it possible to have a continuous process chain. It integrates all functions, from the initial collection of the sample, its transport, homogenization of the tissue, cell disruption right through to the disposal of the remains of the sample. In this way, we avoid the risk of cross-contamination”, reports Hannes Dobler of the IPA. Other advantages of this patented process: it can be automated and helps to minimize the number of subsequent process steps – such as centrifuging.